From the Mariposa trail as it descends, can be seen most of the prominent cliffs which form its massive side walls. This trail reaches the bottom of the valley near its lower extremity. Below this trail, it narrows to a rocky cañon, almost impassable except for the Merced river, which leaves the valley through this gorge. I shall again refer to this cañon in another chapter. The valley is about six miles long and from half a mile to over a mile in width at the head of the valley proper. It is irregular in shape, but its general direction is nearly east towards its upper end. Its outlines will be better understood from a view of the accompanying map, which has been mostly copied from that of the State Geological Survey--Prof. Whitney’s. The three cañons which open into the valley at its upper end, are so intimately connected with it that a general description will include them all, particularly the parts of them in close proximity to the valley. They will be specially described when reached. The sides of the valley are walls of a grayish-white granite, which becomes a dazzling white in a clear sunlight. This intensity of reflection is, however, toned to a great extent by the varying haze which permeates the upper atmosphere of the valley for most of the time. This haze has sometimes the appearance of a light cloud of blue smoke, with its borders fringed with a silvery vapor. At other times--during August and September--the tint is enriched, and at sunrise and sunset for the valley the golden light seems to permeate the haze, and lend its charm to the gossamer film that shields the sight from the glare of the reflecting granite. The walls on each side are in many places perpendicular, and are, from the level of the valley to the top of the cliffs, from 2,660 to 4,737 feet in height, or, as they are generally described, from half a mile to a mile in height. Prof. Whitney, however, says: “The valley is sunk almost a mile in perpendicular depth below the general level of the adjacent region.” This is undoubtedly correct, for in his description, he says: “The Yosemite Valley is nearly in the center of the State, north and south, and just midway between the east and west bases of the Sierras; here a little over seventy miles wide.” Prof. Whitney’s estimate of the depth of the valley must be literally correct, for the general slope of that region is toward the valley, except from the west, its lower end.